When one of my frined enquired about re-qualifcation requirements of LAF for any reason, it was easy to reply - Hey buddy, go for velocity, linearity, leak test(DOP Test), no. of air changes , temperature and humidity. That's true, these are all the requirements when a LAF needs to be re-qualified, say after re-installation, major maintenance or replacement of major component (e.g. blower).
But let's take a deeper look. In fact re-qualification of a LAF should not be taken as differnet from initial qualification. In case of equipment used in sterile areas (or other wise too), the re-qualification should follow the initial qualification protocol or practice. The point is new DQ should meet new user requirments. The other critical attributes such as velocity, linearity, leak test(DOP Test), temperature and humidity (If requirement are specified) must be addressed with acceptance criteria clearly laid down. However, what is important in this case is the area qualification where the re-qualified LAF is (re-) installed. For this routine area monitoring for vialbe and non-viable particluates can be performed.